In a two-class three-dimensional classification find the equation of decision boundary.

I've just started learning Pattern Recognition and I am kind of stuck at this homework assignment, any help will be appreciated. Thank you.

In a two-class three-dimensional classification problem, the feature vectors in each class are normally distributed with same co-variance matrix

 | 0.3  0.1  0.1 |
 | 0.1  0.1 -0.1 |   = Σ  
 | 0.1 -0.1  0.3 | 

The respective mean vectors are [0, 0, 0]t and [0.5, 0.5, 0.5]t. Find the equation of the decision boundary. Assume equal a-priori probabilities.